A hybrid vehicle may be repeatedly stopped and started during the course of a trip to conserve fuel. If the engine is stopped in an undesirable position, it may take longer for the engine to restart. Further, engine emissions may increase if the engine is stopped in an undesirable position. Some engines are stopped by stopping fuel injection at a particular engine position in an effort to stop the engine at a desired position. However, engine operating conditions may vary from engine stop to engine stop so that the engine does not always stop at the desired position. Consequently, the engine may occasionally stop at an undesirable position where engine starting time and emissions may increase.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine stopping method, comprising: adjusting a speed of a driveline integrated starter/generator (DISG) to a desired speed that provides a desired transmission clutch oil line pressure in response to a request to stop engine rotation; and slipping a driveline disconnect clutch in a driveline between the DISG and the engine to stop the engine at a desired position.
By adjusting an a speed of a driveline integrated starter/generator to a speed that provides a desired transmission clutch oil pressure and by slipping a driveline disconnect clutch to stop the engine at a desired position, it may be possible to improve engine stopping. In particular, by adjusting DISG speed to a speed that provides a desired transmission clutch oil pressure, transmission clutches may be applied during engine stopping such that the engine encounters more or less resistance to rotation during engine stopping. Thus, the transmission clutch pressures may be adjusted to control engine stopping position. For example, if engine position is approaching a desired stopping position, transmission clutches may be applied with additional force to tie the transmission output shaft to the transmission case so that some additional resistance may be applied to the engine through the torque converter. Additionally, the torque converter clutch slip may be reduced during engine stopping while the transmission clutches are tying the transmission output shaft to the transmission case. Further, by slipping a driveline disconnect clutch during engine stopping, torque applied to the engine may be varied so that engine stopping position may be adjusted and the engine decelerates to a stop.
The present description may provide several advantages. Specifically, the approach may provide more repeatable engine stopping. Further, the approach may improve engine starting via providing a more consistent engine stopping position. Further still, the approach may reduce engine emissions by stopping the engine at a position that produces less emissions during engine restarting.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.